The need for a coating process which permits application of dosage form coating material on a batch scale yet ultimately results in the exposition of predefined portions of the coated object is well established.
In the pharmaceutical industry, there is a need for a solid dosage form coating process capable of applying a water insoluble and poorly water permeable coating onto a solid dosage form which allows for exposure of predefined portions of the dosage form to the environment of use.
Pending U.S. application Ser. No. 07/815,304, filed Dec. 28, 1991, relies on the discrete application of a coating to predetermined portions of the solid dosage form, to assure proper delivery of medicament over an extended period of time. This coating can be applied manually so as to assure that a particular surface is uncoated or alternatively, the entire tablet can be coated and then drilled to provide a hole through the film coating to expose the surface of the dosage form. Both of these techniques are time consuming, expensive and not amenable to batch processing of tablets.
A procedure to form a passageway in a film coating is taught in U.S. Pat. No. 4,271,113. This patent describes a process for forming an outlet passageway in an osmotic dispensing device by compressing a pin point recess or indentation in the core tablet and then spray coating the core tablet with a wall forming material. The indentation remains partially uncoated. This indentation does not result in the detachment of protective film coating during operation, rather, a permanent hole remains through the film coat after the coating operation is complete.